Senior welfare experts have urged the government to reconsider benefit cuts coming into force next week that will disproportionately hit the poorest families and push a further 200,000 children into poverty.

In an open letter to David Cameron, published in the Guardian, more than 50 social policy professors warn that the welfare reforms, coupled with previous tax, benefit and public expenditure cuts, will result in the poorest tenth of households losing the equivalent of around 38% of their income.

They say the changes will undermine public support for the welfare state – which they call "one of the hallmarks of a civilised society".

"Welfare states depend on a fair collection and redistribution of resources, which in turn rests upon the maintenance of trust between different sections of society and across generations.

"Misleading rhetoric concerning those who have to seek support from the welfare state, such as the contrast between 'strivers' and 'shirkers', risks undermining that trust and, with it, one of the key foundations of modern Britain."

The letter argues that such rhetoric does not reflect the reality of a UK where families move fluidly in and out of work and in and out of poverty.

It adds: "In the interests of fairness and to protect the poorest, as well as to avoid the risk of undermining the consensus on the British welfare state, we urge you to increase taxation progressively on the better off, those who can afford to pay (including ourselves), rather than cutting benefits for the poorest."

A separate report compiled by academics from six UK universities concludes that Britain's poorest are worse off today than they were at the height of the cuts imposed by Margaret Thatcher's Conservative government in 1983.

The Poverty and Exclusion project reports that 33% of British households lacked at least three basic living necessities in 2012, compared with 14% in 1983. These include living in adequately heated homes, eating healthily, and owning basic clothing items such as properly fitting shoes.

"Despite the fact that the UK is a much wealthier country, levels of deprivation are going back to the levels found 30 years ago," says the report, titled The Impoverishment of The UK.

Some of the findings are featured in an ITV Tonight programme titled Breadline Britain on Thursday evening.

The report found:

• Around 4 million adults and almost 1 million children lack at least one basic item of clothing, such as a warm winter coat, while 3 million adults of working age (including over a fifth of those looking for work) cannot afford appropriate clothes for a job interview.

• Roughly 4 million children and adults are not fed properly judged against what most people consider to be a minimally acceptable diet – meaning they do not eat three meals a day, including fresh fruit, meat, fish and vegetables. Over a quarter of all adults skimped on meals so others in their households could eat.

• One-third of all adults can't afford to pay unexpected costs of £500 (such as if a cooker breaks down), 31% can't afford to save at least £20 a month, and 1 million children can't afford to join sports training or drama clubs.

• About 11 million people cannot afford adequate housing conditions and nearly one in ten households are unable to afford to fully heat their home.

The project measures who and how many people fall below what the majority agree are "necessities for life" in the UK today. The list of necessities also includes consumer items such as a washing machine and a telephone, and social activities like visiting friends and family in hospital.

"The results present a remarkably bleak portrait of life in the UK today and the shrinking opportunities faced by the bottom third of UK society," said the head of the project, Professor David Gordon of Bristol University. "Moreover this bleak situation will get worse as benefit levels fall in real terms, real wages continue to decline and living standards are further squeezed."